1. Field of the Invention
The invention relates to a linear actuator that includes at least one attachment for mounting the actuator and an electric control.
2. The Prior Art
Linear electric actuators are widely used in connection with adjustable furniture such as beds, chairs and tables, where they serve to adjust, e.g., the back rest and leg rest section of a bed, or the height of a table. Electric actuators may also advantageously be used in care equipment like, e.g., a patient lift, which serve to lift and lower a patient, e.g., from above and into a chair or a bed.
In connection with the adjustment of furniture and care equipment such as the types mentioned above, personal safety is an area of priority. During the adjustment an actuator produces large forces, which may result in major injuries of patients and staff if a part of the body unintentionally blocks the mechanical adjustment mechanisms. When a patient lift of the crane type consisting of a tower having a cantilever arm for lifting and lowering a patient is concerned, the same problem occurs. To lift a patient, as opposed to lowering the patient, requires that the actuator exercises a power. However, it is during the lowering that a risk for squeeze injuries occurs. Particularly, squeeze injuries may occur as the cantilever arm of the patient lift, after the patient has been brought into contact with the base, continues to move downwards, hits the patient and performs an increasing pressure on the patient, resulting in injuries. The same applies to beds and chairs where lowering of a sitting or lying surface may cause squeeze injuries.
U.S. Pat. No. 6,201,481 to Okin discloses a safety device for electrically-adjustable articles of furniture wherein a trapped object will activate a switch in the form of a squeezing list, which subsequently cuts off the current to the actuator. The arrangement requires that squeezing lists are mounted on all the surfaces where a risk of squeezing exists. On a bed that would typically be between the bed frame and the back rest and leg rest sections. The solution is expensive and not particularly reliable.
U.S. Pat. No. 4,407,030 to Maxwell Products, Inc. discloses a safety device for an adjustable bed where a back rest section and a leg rest section may be adjusted by means of a linear actuator each. By means of the rear attachment, the actuators are secured to the bed construction with a shaft led through an oblong hole. At one end of the hole, a switch is located. During normal operation, the shaft is pulled forward in the hole free of the switch. If something is trapped between the back rest section and the bed frame, the shaft will be pushed backwards in the oblong hole and thus activate the switch for cutting off the current for the motor. The arrangement provides a useful solution to the problem but is not practical since the switch is mounted as a separate attachment, which should be fitted individually and requires a cable connection to either the actuator or the control. Such a cable connection is not only difficult and expensive but also vulnerable to mechanical damages.
A solution is therefore needed which in a safe and simple manner solves the problem of squeeze injuries during adjustment of the aids and articles of furniture mentioned above.
The purpose of the invention is to provide a simple solution to the outlined problem.